Mobile communication devices are commonly used in today's society. Most of these devices are capable of telecommunication using at least one network. Many of the newer mobile devices are now capable of telecommunication using multiple networks. The ability to switch between multiple networks in an efficient manner is essential for these newer devices. Future multiple networks are expected to combine several different radio-access technologies, such as 3G cellular, WLAN, and WiMax. This variety of access options gives a user with a multi-interface device the possibility of being “always best connected”, using ‘vertical’ handoffs between the heterogeneous network technologies.
Vertical handoff is the process by which a mobile device switches between two different networks.
Traditional handover algorithms are based on a single attribute, signal strength, and handover policies are threshold based. These thresholds are easily determined based on physical parameters, including appropriate margins to avoid hysteresis.
However, traditional methods are not able to adapt to multiple criteria, dynamic user preferences, and changing network availability.
Several methods have been proposed to deal with multiple criteria, which rely on definition of an appropriate cost function, utility function, or weighting of different metrics. The number of different parameters involved can be large, and these parameters must often be completely specified by an expert ahead of time. Additionally, often the different parameters are not always available for a given network. Furthermore, when preferences change, the algorithm does not.
Therefore, there is a need for a network selection and vertical handover, which can adapt to dynamically changing preferences and environmental conditions of the networks.